Clinton down, but not out of running

"Convincingly" means by double-digits, he says. Then Clinton would have to pull off an upset in North Carolina (May 6) or Oregon (May 20), where Obama is favored. "Most people looking at the last 10 events or so see a bit of an edge for Clinton, but with Obama having significant places to look for wins as well," Mr. Jillson adds.

For now, though, the trends seem to be heading in Obama's direction – even in Pennsylvania, where polls showed Clinton with a lead in the mid-to-high teens until recently. The latest Quinnipiac Poll shows Clinton with a nine-point lead in Pennsylvania, a figure that makes sense to political analysts in the state.

Pennsylvania's demographics – large populations of working-class, older, and Roman Catholic voters – play to Clinton's advantage. But a wave of new registrations in the state could spell trouble for her, as the Obama campaign has worked hard to identify new voters. "[Pennsylvania] is absolutely critical for her," says Terry Madonna, head of the Franklin and Marshall College Poll. "I think she wins here, but for the first time, I'm thinking he could upset her. It's a long-shot, but I see a way."